1. Field of the Invention
The present invention relates, in general, to semiconductor device packaging and, in particular, to printed circuit board (PCB) substrates and methods for their manufacture.
2. Description of the Related Art
Printed Circuit Board (PCB) substrates serve as a base for the mechanical support and electrical interconnection of semiconductor devices (e.g., integrated circuits). FIG. 1 is a simplified cross-sectional diagram of a portion of a conventional PCB substrate 10. Conventional PCB substrate 10 includes a sheet-like base 12 formed of an electrically non-conductive composite material (e.g., a glass material with epoxy resin). Sheet-like base 12 has an upper surface 14 and a lower surface 16. Conventional PCB substrate 10 also includes a plurality of electrically conductive vias 18 (only one of which is shown in FIG. 1) that extend from upper surface 14 to lower surface 16.
Conventional PCB substrates are typically manufactured by initially forming a sheet-like base of non-conductive material. The sheet-like base can be formed, for example, by weaving glass fibers into a sheet of cloth. The sheet of cloth is then dipped in resin and thermally cured to form the sheet-like base. Thereafter, via holes are mechanically drilled through the sheet-like base, plated and filled with an electrically conductive material (e.g., copper) to form electrically conductive vias. The mechanical drilling, plating and filling steps of such a conventional process are expensive, have a low throughput and result in a low yield. This is especially so when a PCB substrate with a large number of electrically conductive vias and/or electrically conductive vias of small diameter is being manufactured. Furthermore, the act of mechanically drilling through the sheet-like base, by itself, can inadvertently decrease the mechanical stability of the PCB substrate.
Still needed in the field, therefore, is an inexpensive and high throughput method for manufacturing a PCB substrate. In addition, the method should result in a high PCB substrate yield and a PCB substrate of high mechanical stability.
The present invention provides an inexpensive and high throughput process for manufacturing a PCB substrate. In addition, the process has a high PCB substrate yield and produces a PCB substrate of high mechanical stability.
A process according to one exemplary embodiment of the present invention includes first weaving a plurality of electrically non-conductive strands (e.g., fiberglass yarns) and at least one electrically conductive strand (e.g., a copper wire) to form a woven fabric. Upper and lower surfaces of the woven fabric thus formed are exposed.
Next, the woven fabric is impregnated with a resin material to form an impregnated fabric and, thereafter, the impregnated fabric is cured to form a cured fabric. The upper and lower surfaces of the cured fabric are then planed. The planing of these surfaces segments the at least one electrically conductive strand and forms a PCB substrate. The PCB substrate formed by the planing step includes a planarized cured fabric with an upper planed surface, a lower planed surface and a plurality of electrically conductive strand segments extending from the upper planed surface to the lower planed surface. Since each of the electrically conductive strand segments extends from the upper planed surface to the lower planed surface, the electrically conductive strand segments are configured to function as electrically conductive vias in the PCB substrate.
Weaving is a reliable, inexpensive and high throughput process technology in comparison to the mechanical drilling, plating and filling technologies used in conventional PCB substrate manufacturing. Therefore, processes according to the present invention provide for the inexpensive, high throughput and high yield manufacturing of PCB substrates.
The present invention also provides a PCB substrate having a planarized woven fabric with a cured resin material impregnated therein. The planarized woven fabric includes an upper planed surface, a lower planed surface and a plurality of integrally formed electrically conductive strand segments (e.g., copper wire segments) extending from the upper planed surface to the lower planed surface. Since the electrically conductive strand segments were formed integrally with the remainder of the planarized woven fabric, PCB substrates according to the present invention are of high mechanical stability.